This page tests whether or not the background shorthand properly omits initial values.

PASS: document.body.style.background == 'green' should be true and is.
PASS: document.getElementById('div1').style.background == 'repeat-x, repeat-y white' should be true and is.
PASS: document.getElementById('div2').style.background == '50% 50% blue' should be true and is.
PASS: document.getElementById('div3').style.background == 'none repeat scroll rgb(255, 255, 255)' should be true and is.